Highly stable fuel cell membranes and methods of making them

ABSTRACT

A solid polymer electrolyte membrane having (a) an ion exchange material and (b) dispersed in said ion exchange material, a hydrogen peroxide decomposition catalyst bound to a carbon particle support, wherein the hydrogen peroxide decomposition catalyst comprises (i) polyvinylphosphonic acid and (ii) cerium.

FIELD OF THE INVENTION

The present invention relates to highly stable membranes for use inpolymer electrolyte membrane fuel cells and methods of making same.

BACKGROUND OF THE INVENTION

Fuel cells are devices that convert fluid streams containing a fuel (forexample, hydrogen) and an oxidizing species (for example, oxygen or air)to electricity, heat, and reaction products. Such devices comprise ananode, where the fuel is provided, a cathode, where the oxidizingspecies is provided, and an electrolyte separating the two. As usedherein, the term “catalyst coated membrane” means a combination of anelectrolyte and at least one electrode. The fuel and oxidant aretypically liquid or gaseous materials. The electrolyte is an electronicinsulator that separates the fuel and oxidant. It provides an ionicpathway for the ions to move between the anode, where the ions areproduced by reaction of the fuel, to the cathode, where they are used toproduce the product. The electrons produced during formation of the ionsare used in an external circuit, thus producing electricity. As usedherein, fuel cells may include a single cell comprising only one anode,one cathode and an electrolyte interposed therebetween, or multiplecells assembled in a stack. In the latter case there are multipleseparate anode and cathode areas wherein each anode and cathode area isseparated by an electrolyte. The individual anode and cathode areas insuch a stack are each fed fuel and oxidant, respectively, and may beconnected in any combination of series or parallel external connectionsto provide power.

Additional components in a single cell or in a fuel cell stack mayoptionally include means to distribute the reactants across the anodeand cathode, including, but not limited to porous gas diffusion media.Various sealing materials used to prohibit mixing of the various speciesmay also be used. As used herein, the membrane electrode assembly (MEA)comprises the catalyst coated membrane and such gas diffusion media andsealing materials. Additionally, so-called bipolar plates, which areplates with channels to distribute the reactant may also be present.

A Polymer Electrolyte Membrane Fuel Cell (PEMFC) is a type of fuel cellwhere the electrolyte is a polymer electrolyte. Other types of fuelcells include Solid Oxide Fuel Cells (SOFC), Molten Carbonate Fuel Cells(MCFC), Phosphoric Acid Fuel Cells (PAFC), etc. As with anyelectrochemical device that operates using fluid reactants, uniquechallenges exist for achieving both high performance and long operatingtimes. In order to achieve high performance it is necessary to reducethe electrical and ionic resistance of components within the device.Recent advances in the polymer electrolyte membranes have enabledsignificant improvements in the power density of PEMFCs. Steady progresshas been made in various other aspects including lowering Pt loading,extending membrane life, and achieving high performance at differentoperating conditions. However, many technical challenges are stillahead. One of them is for the membrane electrode assembly to meet thelifetime requirements for various potential applications. These rangefrom hundreds of hours for portable applications to 5,000 hours orlonger for automotive applications to 40,000 hours or longer instationary applications.

Although all of the materials in the fuel cell may be subject todegradation during operation, the integrity and health of the membraneis particularly important. Should the membrane degrade during fuel celloperation, it tends to become thinner and weaker, thus making it morelikely to develop holes or tears. Should this occur, the oxidizing gasand fuel may mix internally potentially leading to internal reaction.Because such an internal reactions may ultimately cause damage to theentire system, the fuel cell must be shut down. One well known approachto assessing the health of fluorinated membranes is to measure theamount of fluoride ions in the product water of the fuel cell. Highervalues of this so-called fluoride release rate are indicative of moreattack of the membrane, and therefore are associated with membranes thathave lower durability. Correspondingly, lower fluoride release rates areindicative of a healthier membrane, one more likely to have longer life.

As is well known in the art, decreasing the thickness of the polymerelectrolyte membrane can reduce the membrane ionic resistance, thusincreasing fuel cell power density. However, reducing the membranesphysical thickness can increase the susceptibility to damage from otherdevice components leading to shorter cell lifetimes. Variousimprovements have been developed to mitigate this problem. For example,U.S. Pat. No. RE 37,307, U.S. Pat. No. RE37,701, US Application No.2004/0045814 to Bahar et al., and U.S. Pat. No. 6,613,203 to Hobson, et.al. show that a polymer electrolyte membrane reinforced with a fullyimpregnated microporous membrane has advantageous mechanical properties.Although this approach is successful in improving cell performance andincreasing lifetimes, it does not address mechanisms involving chemicalattack of the membrane by highly oxidizing species present during fuelcell operation. These include, for example, various radical species suchas peroxide and hydroxide radicals that can attack and degrade theionomer. Thus, the mechanical reinforcement in '307 and the like is anecessary, but generally not totally sufficient, condition for longerlife.

The performance of a fuel cell over time is known as fuel celldurability, or fuel cell stability. During normal operation of a fuelcell, the power density typically decreases as the operation timeincreases. This decrease, described by practitioners as voltage decay,is not desirable because less useful work is obtained as the cell agesduring use. Ultimately, the cell or stack will eventually produce solittle power that it is no longer useful at all. Furthermore, duringoperation the amount of fuel, for example, hydrogen, that crosses overfrom the fuel side to the oxidizing side of the cell will increase asthe health of the membrane deteriorates. Hydrogen cross-over is thusused as one measure of membrane life.

A life test is generally performed under a given set of operatingconditions for a fixed period of time. The test is performed under aknown temperature, relative humidity, flow rate and pressure of inletgases. In the present application, life tests are performed under opencircuit conditions because these are known in the art to give the mostaccelerated membrane degradation. Thus, if a membrane has limited or nodegradation during an open circuit voltage hold, it can be expected tolast a much longer time when used in an actual fuel cell under load.

As mentioned above, hydrogen cross-over and fluoride release rate aretypically used to determine the extent of degradation, and thereby life,of a fuel cell. For hydrogen cross-over, the amount of hydrogen thatcrosses over from one side of the membrane to the other is measuredafter at various times during a life-test. If the hydrogen cross-over isabove some predetermined level, 2.5 cm³ H₂/min is used herein, then thetest is ended, and the life is calculated as the number of hours thecell has operated. Fluoride release rate (FRR) measures degradationproducts that leave the cell in the product water during a life test.For fluorocarbon membranes, the amount of fluoride ions in the water canbe measured, and the rate of production of them is calculated as afluoride release rate. The lower this number, the less degradation andtherefore the longer the membrane will survive, at least assuming thedegradation is uniform in the membrane. (Specific details of the testprotocol used herein for life determination are described below).

Although there have been many improvements to fuel cells in an effort toimprove life of fuel cells, there continues to be an unmet need for evenmore durable fuel cells, and in particular, more durable membranematerials for use in PEMFCs.

SUMMARY OF THE INVENTION

The present invention provides compound for increasing the durability ofa fuel cell membrane. The compound includes an organic polymer includinga monomer with at least two carbon atoms and at least one moietycomprising phosphorous, and a metal that is a transition metal withmultiple oxidation states or a lanthanide metal with multiple oxidationstates. Preferably, the organic polymer is polyvinylphosphonic acid(PVPA). Also preferably, the organic polymer is a noncrystalline polymerinsoluble in strong acid. The metal is preferably cerium. Preferably,the compound is bound to a support particle which is preferably carbon,but in alternative embodiments is alumina or silica or zeolite. Theinventive compound is a composition of matter comprising the reactionproduct of PVPA, cerium (III) nitrate hexahydrate, and water.Alternatively, the invention is a composition of matter comprising thereaction product of carbon black, PVPA, Ce(NO₃)₃6H₂O, and water.

In another aspect, the invention provides a membrane including thecompound described herein. The inventive solid polymer electrolyte ofthis aspect of the invention includes (a) an ion exchange material and(b) dispersed in said ion exchange material, a hydrogen peroxidedecomposition catalyst bound to a carbon particle support, wherein thehydrogen peroxide decomposition catalyst comprises (i)polyvinylphosphonic acid and (ii) cerium. Preferably, the solid polymerelectrolyte membrane further includes expanded polytetrafluoroethylenehaving a porous microstructure of polymeric fibrils, and the ionexchange material impregnated throughout the porous microstructure ofthe expanded PTFE membrane so as to render an interior volume of theexpanded PTFE membrane substantially occlusive. Also preferably, thesolid polymer electrolyte membrane includes a first layer comprising (a)at least one expanded PTFE membrane having a porous microstructure ofpolymeric fibrils, and (b) at least one ion exchange materialimpregnated throughout the porous microstructure of the expanded PTFEmembrane so as to render an interior volume of the expanded PTFEmembrane substantially occlusive, and a second layer comprising ionexchange material in the absence of an expanded PTFE membrane. Thesecond layer preferably includes the peroxide decomposition catalyst.

In another aspect, the invention provides an electrode including thecompound described herein. The inventive electrode of this embodimentincludes (a) an ion exchange material; (b) an organic polymer includinga monomer with at least two carbon atoms and at least one moietyincluding phosphorous, (c) a metal including a transition metal withmultiple oxidation states or a lanthanide metal with multiple oxidationstates, and (d) a catalyst for either fuel oxidation or oxygenreduction.

In another aspect, the invention provides a catalyst coated membraneincluding the compound described herein. The inventive catalyst coatedmembrane of this embodiment includes (a) at least one electrode capableof oxidizing a fuel or reducing an oxidant, (b) a solid polymerelectrolyte attached to the electrode wherein the solid polymerelectrolyte or electrode includes an (1) ion exchange material and (2) aperoxide decomposition catalyst, wherein the peroxide decompositioncatalyst comprises an organic polymer comprising at least two carbonatoms and at least one a moiety comprising phosphorous, and (ii) a metalcomprising a transition metal with multiple oxidation states or alanthanide metal with multiple oxidation states.

In another aspect, the invention provides a fuel cell including thecompound described herein. The inventive fuel cell of this embodimentincludes (a) an anode comprising a catalyst for oxidizing fuel,

(b) a cathode comprising a catalyst for reducing an oxidant, and

(c) a solid polymer electrolyte;

wherein at least one of the solid polymer electrolyte, the anode and thecathode comprises a peroxide decomposition catalyst comprising anorganic polymer comprising at least two carbon atoms and a moietycomprising phosphorous, and (ii) a metal comprising a transition metalwith multiple oxidation states or a lanthanide metal with multipleoxidation states.

(d) a fuel supplied to the anode;

(e) an oxidant supplied to the cathode.

In another aspect, the invention provides various methods to prepare theinventive compounds, SPEM, electrodes, CCMs and fuel cells. One suchembodiment is a method to make a compound comprising the steps of

(1) preparing an organic polymer comprising at least two carbon atoms insolution;

(2) adding a salt of a metal selected from the group of transitionmetals and lanthanides that have multiple oxidation states,

(3) precipitating said compound.

The method may further comprise a step 1A after step 1 wherein a supportparticle is added to said solution; additional step or steps after step3 to separate the compound, to purify the compound, for example by acidwashing, and to dry the compound.

Further embodiments of the invention are methods such as those describedabove where a support particle is also added in step 1, where thesupport particle may include, but is not limited to alumina, silica,zeolite and carbon. Additionally, the solution used in step 1 maycomprise an ion exchange material. Further embodiments of the inventivemethod include steps in addition to those described above to prepare anelectrode comprising the compound, or preparing a SPEM comprising thecompound, or preparing a CCM where the compound is present in one ormore of the electrodes and membrane.

DESCRIPTION OF THE DRAWINGS

The operation of the present invention should become apparent from thefollowing description when considered in conjunction with theaccompanying figure.

FIG. 1 is a drawing illustrating several embodiments of the inventivesolid polymer electrolytes.

FIG. 2 is a drawing illustrating additional embodiments of the inventivesolid polymer electrolytes.

FIG. 3 is a drawing illustrating further embodiments of the inventivesolid polymer electrolytes.

FIG. 4 is a drawing illustrating yet additional embodiment of theinventive solid polymer electrolytes.

FIG. 5 schematically illustrates an embodiment of the inventive methodfor preparing the inventive solid polymer electrolytes.

FIG. 6 is a drawing of a fuel cell that uses the inventive solid polymerelectrolyte.

FIG. 7 is another embodiment of the invention of an inventive electrodefor use in a solid polymer electrolyte fuel cell.

FIG. 8 is a drawing of a fuel cell that uses another embodiment of theinventive solid polymer electrolyte.

DETAILED DESCRIPTION OF THE INVENTION

Inventors have discovered compounds, which when used as a component insolid polymer electrolyte (SPE) membranes, in electrodes, or in catalystcoated membranes in fuel cells, surprisingly significantly reducemembrane degradation and give a concomitant increase in membrane life.The inventive compounds are catalysts capable of peroxide decompositionand are formed of a metal, preferably cerium, and an organic polymermade from a monomer having at least 2 carbon atoms, preferably PVPA,bound to the support particles. When used as a component in a compositemembrane, the combination of the low levels of supported peroxidedecomposition catalyst and the phosphorous containing compound thatbinds the peroxide decomposition catalyst to the support yields a verystable membrane that has surprisingly very long life when used in aPEMFC. Furthermore, the inventive compositions do so at surprisingly lowtransition metal levels (<1 wt. percent), and quite unexpectedly,largely without the deleterious effects of loss of power density andtransient power effects often associated with prior art using theaddition of transition metals or transition metal compounds to themembrane. Various embodiments of the inventive SPEs are described below.

FIG. 1 shows a schematic of a three different embodiments of theinventive solid polymer electrolyte 10. SPE 10 typically is thin, lessthan 100 microns, preferably less than 75 microns, and most preferablyless than 40 microns thick. It comprises an ion exchange material 11that is able to conduct hydrogen ions at a high rate in typical fuelcell conditions. The ion exchange materials may include, but are notlimited to compositions comprising phenol sulfonic acid; polystyrenesulfonic acid; fluorinated-styrene sulfonic acid; perfluorinatedsulfonic acid; sulfonated Poly(aryl ether ketones); polymers comprisingphthalazinone and a phenol group, and at least one sulfonated aromaticcompound; aromatic ethers, imides, aromatic imides, hydrocarbon, orperfluorinated polymers in which ionic an acid functional group orgroups is attached to the polymer backbone. Such ionic acid functionalgroups may include, but are not limited to, sulfonic, sulfonimide orphosphonic acid groups. Additionally, the ion exchange material 11 mayfurther optionally comprise a reinforcement to form a compositemembrane. Preferably, the reinforcement is a polymeric material. Thepolymer is preferably a microporous membrane having a porousmicrostructure of polymeric fibrils, and optionally nodes. Such polymeris preferably expanded polytetrafluoroethylene, but may alternativelycomprise a polyolefin, including but not limited to polyethylene andpolypropylene. An ion exchange material is impregnated throughout themembrane, wherein the ion exchange material substantially impregnatesthe microporous membrane to render an interior volume of the membranesubstantially occlusive, substantially as described in Bahar et al,RE37,307, thereby forming the composite membrane.

The SPE 10 of FIG. 1 also comprises a plurality of particles 14supporting a peroxide decomposition catalyst, preferably a compound ofcerium and PVPA. Particles 14 are dispersed in a substantially airocclusive, electronically insulating ionomer layer 13 adjacent to thesurface of ion exchange material 11. A plurality of the particles 14preferably have a size less than about 75 nm, or preferably less thanabout 50 nm. The peroxide decomposition catalyst is bound to theparticles. Although PVPA is preferred, other organic polymers comprisingphosphorus are contemplated according to this invention. Preferably, theorganic polymer is substantially insoluble in the acid environment ofthe ionomer membrane. In alternative embodiments, the compound includesorganic dihydrogen phosphonate compounds, polystyrenephosphonic acid,poly-alpha, beta, beta-trifluorostyrenephosphonic acid, orpolyvinylbenzyl phosphonic acid. Using the inventive composition, theperoxide decomposition catalyst appears to be substantially immobileduring fuel cell operation, as may be demonstrated by electronmicroprobe analysis. In other words, the metal or metal ions associatedwith the peroxide decomposition catalyst do not substantially dissolveor move within the membrane during fuel cell operation. By so doing, anyreduction in power density during fuel cell operation or other transienteffects observed in prior art that uses unsupported, or unbound,catalyst compounds or catalyst ions (e.g., Ce or Mn, or compoundsthereof) is avoided. Furthermore, the complexing of the metal such ascerium with the polymer such as PVPA changes the reduction potential ofthe cerium, such that it is a more effective peroxide decompositioncatalyst.

Such particles 14 may be agglomerated together in groups of two, threeor even in larger groupings of many particles, though it is preferablethat they are separated in smaller clusters of a few particles, and mostpreferably, as individual particles. Layer 13 may be only on one side ofthe ion exchange material 11 (FIG. 1 a and 1 b) or on both sides (FIG. 1c). Preferably, it is used on the side facing the cathode (not shown).Optionally, a second ion exchange material 12 may also be present (FIG.1 b) on the side opposite layer 13. The composition of ion exchangematerial 12 may be the same as ion exchange material 11, or it may be ofa different composition. Similarly. layer 13 may be the same ionexchange material as ion exchange material 11, or it may be a differentcomposition. The peroxide decomposition catalyst may include anynon-precious metal catalyst known in the art that is capable ofcatalyzing peroxide decomposition. Preferred peroxide decompositioncatalysts include metals that decompose hydrogen peroxide to water inacid conditions with either limited or no release of radical speciesthat could potentially initiate polymer decomposition. These include,but are not limited to, metal and metal oxide ions, or other speciescontaining cations of transition metals or lanthanides that havemultiple oxidation states and are not electrochemically too active. Suchmaterials may include, but are not limited to, Ti, VO, Cr, Mn, Fe, Co,Cu, Ag, Eu, Pr, Tb and Ce. [see for example, Table 9, pg. 123 in Stukul,Giorgio, in chapter 6, “Nucleophilic and Electrophilic Catalysis withTransition Metal Complexes” of Catalytic Oxidations with HydrogenPeroxide as Oxidant, Stukul, Giorgio (ed.), Kluwer Academic Press,Dordrecht, Netherlands, 1992]. Of these, however, as shown in theexperimental results below, cerium has shown the most surprisingresults.

FIGS. 2-4 schematically illustrate alternative approaches for theinventive solid polymer electrolyte. In FIG. 2, the solid polymerelectrolyte 10 has a plurality of particles 14 supporting a peroxidedecomposition catalyst within a composite membrane 21 having an expandedPTFE membrane having a porous microstructure of polymeric fibrils, andion exchange material impregnated throughout the porous microstructureof the expanded PTFE membrane so as to render an interior volume of theexpanded PTFE membrane substantially occlusive. Additionally, asubstantially air occlusive, electronically insulating layer 13 may beadjacent to one (FIG. 2 b) or both (FIG. 2 c) surfaces. Optionally, asecond ion exchange material 12 of the same, or of a differentcomposition than used in 21 may also be present (FIG. 1 b) on the sideopposite layer 13. Alternatively, ion exchange material 11, ion exchangematerial 12, composite membrane 21, and substantially air occlusive,electronically insulating ionomer layer 13 may also be present invarious alternating arrangements, some examples of which areschematically in FIG. 3 a-FIG. 3 g and FIG. 4 a-FIG. 4 e. As describedabove, the peroxide decomposition catalyst is bound to the particles bythe compound comprising phosphorus.

The particles 14 shown schematically in FIGS. 1-4 comprise a supportmaterial onto which catalyst has been deposited. The support materialmay comprise silica; zeolites; carbon; and oxides and carbides of thegroup IVB, VB, VIB VIIB, and VIII transition metals; and combinationsthereof. Carbon is a particularly preferable support material. Theypreferably have high surface area, and so should be small in size, lessthan 75 nm, or preferably less than 50 nm, or less than 25 nm. They mayalso optionally be porous. The use of high surface area supports isparticularly advantageous because it allows the peroxide decompositioncatalyst to be highly dispersed, leading to higher catalytic activityper unit weight compared with an unsupported, lower surface areacatalysts of the same composition.

An inventive method for preparing an air occlusive integral compositemembrane has also been discovered. The method comprises the steps of (a)preparing a peroxide decomposition catalyst bound to a support particlewith a compound comprising phosphorus; (b) preparing an ink solutioncomprising the species from part (a) and an ion exchange material; (c)providing a polymeric support having a microstructure of micropores; (d)applying either the ink solution or a solution comprising an ionexchange resin to the polymeric support; (e) optionally, repeating step(d); wherein at least one application in step (d) or (e) uses the inksolution. In this application, an ink is considered to be a solutioncontaining a catalyst on a supporting particle that is dispersed in asolvent. The ink solution preferably also contains an ion exchangepolymer. Solvents used in the ink are those generally known in the art,including but not limited to alcohols, such as ethanol and propanol, orother organic solvents. The preparation of the ink solution preferablyuses a high shear mixer, where the high shear mixer may include, but isnot limited to, microfluidizers, and rotor-stator mixers comprising atleast one stage. Particularly preferable high shear mixers aremicrofluidizers capable of operating at pressures between 5.000 psi and25,000 psi. The ink is preferably very well mixed, which may beaccomplished by one, two, three or more passes through the high shearmixer. The concentration of the peroxide decomposition catalyst in theink is between about 0.01% and about 3% by dry weight of the ionexchange material, and preferably less than 1%, more preferably betweenabout 0.01% and about 0.5%, and most preferably about 0.2%. This ink maybe prepared in one, two or more separate steps if desired. If it isprepared in two or more steps, a more concentrated solution is made inthe first step, and subsequent steps are dilutions with ion exchangematerial and/or solvent to arrive at the final desired concentration.When more than one step of preparing the ink is used, the high shearmixing step described above may be used in one or more of the inkpreparation steps. If desired, the first step in a multi-step inkpreparation process may be accomplished in advance of the succeedingsteps, in which case the ink may be stored for a period of time. If sucha concentrated ink is stored for longer than about 30-60 minutes, thenthe high shear mixing step is preferably repeated at least once, andmore preferably two or three times before any subsequent dilution stepsneeded to arrive at the final ink used for subsequent processing.

Additional steps to remove large agglomerates in the ink solution mayalso be performed, if desired, at any stage during the ink preparation.Such steps may include, but are not limited to, filtering and using acentrifuge. In either case, the number of large particles removed can becontrolled. In the former, by the particular filter chosen; in thelatter, by the length of time the sample is centrifuged, and/or thespeed of the centrifuge. The centrifuge speed may be varied from betweena few hundred rpm, to many thousand rpm, with the higher speeds beingpreferable. The time to centrifuge may vary from a few minutes to anhour or longer. Shorter times at higher speeds, for example less than 30minutes at 3000-5000 rpm, are preferable to reduce processing times.

In a further embodiment of the method, an additional step prior to step(a) may be included, where such step or steps comprise cleaning one ormore of the components used in the method to remove impurities. Suchimpurities may degrade the performance of either the ionomer, or thecatalyst in the electrode, or the peroxide decomposition catalyst. Thecleaning steps may include, but are not limited to washing with hot orcold water, hot or cold acids, sohxlet extractions, heat treatments inappropriately chosen gas atmospheres, or other chemical treatments knownin the are that will remove potentially detrimental impurities. Forexample, a hot acid wash has been found to be preferably when PVPA isused as the compound comprising phosphorus.

The ion exchange material in the ink may be any known in the art, forexample those described above for ion exchange material 11. The peroxidedecomposition catalyst on a supporting particle may be any of thosedescribed above. The compound comprising phosphorus used to bind thecatalyst to the support particle may be any of those described above.

The polymeric support having a microstructure of micropores, may be anysuch material known in the art, including but not limited to microporouspolyethylene, polypropylene or polytetrafluoroethylene. A particularlypreferable polymeric support is expanded PTFE, such as those describedin U.S. Pat. No. 3,953,566 to Gore, or in U.S. Pat. No. 5,814,405 toBranca, et. al.

The ink solution or a solution comprising an ion exchange resin may beapplied to the polymeric support using any process known in the art,including but not limited to the process described in U.S. Pat. No.RE37,707 to Bahar et. al. Another embodiment of the method of theinvention for applying the ink to the polymeric support is shown in FIG.5. In this embodiment, an ink is applied to a thin polymer film 54 usingany means known to one of ordinary skill in the art, for example using apump, syringe 53 or such. The ink is prepared as described above, so maybe prepared in a multistep process starting with a concentrated ink thatis subsequently diluted, or directly in one step to obtain the desiredcatalyst concentration in the ink. The applied ink 52 is then spreadinto a thin layer 56 using any means known in the art for making a thinliquid layer, including but not limited to a draw bar or meyer bar,shown schematically in FIG. 5 as 51. Subsequently, the polymeric support55 having a microstructure of micropores is placed on the liquid layer56 and allowed to imbibe. The thin polymer film 54 comprisespolyethylene, polyethylene terephthalate polypropylene, poly vinylidenechloride, polytetrafluoroethylene, polyesters, or combinations thereof,and may further comprise a coating of a release material, for example afluoropolymer compound, to enhance the release of the final product fromthe polymer film. After the film is completely imbibed, it is allowed todry, and may optionally be heated to decrease the drying time. Suchheating, shown schematically in FIG. 5 as 57, may be accomplished withany means known in the art, including but not limited to forced airheaters, ovens, infrared driers and the like. The process may berepeated if desired, using the same or a different ink, or the same or adifferent ion exchange resin.

When the imbibing steps are completed, an additional heating step at anelevated temperature may optionally be applied using an oven, infraredheater, forced air heater or the like. The temperature of this heatingstep is between about 100° C. and about 175° C. and preferably betweenabout 120 degrees C. and about 160° C. The solid polymer electrolyte isheld at the elevated temperature for between about 1 minute and about 10minutes, and preferably for between about 1 minutes and about 3 minutes.Finally, the completed solid polymer electrolyte membrane is cooled, andremoved from the thin polymer film before use. The removal may beaccomplished by simply pulling the SPE off the thin polymer film, eitherin air or in water.

As is well understood by one of ordinary skill in the art, the processdescribed above and in FIG. 5 can by automated using roll goods, andautomated pay-off and collection systems so that each step isaccomplished in a continuous fashion, and the final product is a roll ofsolid polymer electrolyte supported on a thin polymer film.

The solid polymer electrolyte of the instant invention may also be usedto form a catalyst coated membrane (CCM) using any methods known in theart. In FIG. 6, the CCM 60 comprises an anode 61 of a catalyst foroxidizing fuel, a cathode 62 for reducing an oxidant, and the solidpolymer electrolyte 10 described above interposed between the anode andcathode, on a supporting particle, or directly on the SPE, or from acatalyst-containing ink solution containing the catalysts that isdeposited either directly on the SPE, or on a film that is subsequentlyused in a lamination step to transfer the electrode to the SPE.

The anode and cathode electrodes comprise appropriate catalysts thatpromote the oxidation of fuel (e.g., hydrogen) and the reduction of theoxidant (e.g., oxygen or air), respectively. For example, for PEM fuelcells, anode and cathode catalysts may include, but are not limited to,pure noble metals, for example Pt, Pd or Au; as well as binary, ternaryor more complex alloys comprising the noble metals and one or moretransition metals selected from the group Ti, V, Cr, Mn, Fe, Co, Ni, Cu,Zn, Y, Zr, Nb, Mo, Ru, Rh, Ag, Cd, In, Sn, Sb, La, Hf, Ta, W, Re, Os,Ir, Tl, Pb and Bi. Pure Pt is particularly preferred for the anode whenusing pure hydrogen as the fuel. Pt—Ru alloys are preferred catalystswhen using reformed gases as the fuel. Pure Pt is a preferred catalystfor the cathode in PEMFCs. The anode and cathode may also, optionally,include additional components that enhance the fuel cell operation.These include, but are not limited to, an electronic conductor, forexample carbon, and an ionic conductor, for example a perfluorosulfonicacid based polymer or other appropriate ion exchange resin.Additionally, the electrodes are typically porous as well, to allow gasaccess to the catalyst present in the structure.

A fuel cell 63 can also be formed from the instant invention. As shownin FIG. 6, such PEM fuel cells 63 comprise the CCM 60 and may optionallyalso include gas diffusion layers 64 and 65 on the cathode 62 and anode61 sides, respectively. These GDM function to more efficiently dispersethe fuel and oxidant. The fuel cell may optionally comprise plates (notshown in FIG. 7) containing grooves or other means to more efficientlydistribute the gases to the gas diffusion layers. As is known in theart, the gas diffusion layers 64 and 65 may optionally comprise amacroporous diffusion layer as well as a microporous diffusion layer.Microporous diffusion layers known in the art include coatingscomprising carbon and optionally PTFE, as well as free standingmicroporous layers comprising carbon and ePTFE, for example CARBEL® MPgas diffusion media available from W. L. Gore & Associates. The fluidsused as fuel and oxidant may comprise either a gas or liquid. Gaseousfuel and oxidant are preferable, and a particularly preferable fuelcomprises hydrogen. A particularly preferable oxidant comprises oxygen.

Another embodiment of the invention (illustrated in FIG. 7) is anelectrode 70 for use in a solid polymer electrolyte fuel cell, where theelectrode comprises (a) an ion exchange material 75 (b) a plurality ofparticles 14 supporting a peroxide decomposition catalyst, and (c) acompound comprising phosphorus that binds said peroxide decompositioncatalyst to said particles. In this embodiment it is understood that theelectrode 70 can either be used as an anode or a cathode in a SPEFC. Itwill include appropriate catalysts 71 known in the art for fueloxidation and oxygen reduction, respectively. These may include, but arenot limited to precious metals such as supported or unsupported Ptand/or Pt alloys and the like, such as those described above for 61 and62 of FIG. 6. The ion exchange material 72 may include, but is notlimited to compositions comprising phenol sulfonic acid; polystyrenesulfonic acid; fluorinated-styrene sulfonic acid; perfluorinatedsulfonic acid; sulfonated Poly(aryl ether ketones); polymers comprisingphthalazinone and a phenol group, and at least one sulfonated aromaticcompound; aromatic ethers, imides, aromatic imides, hydrocarbon, orperfluorinated polymers in which ionic an acid functional group orgroups is attached to the polymer backbone. Such ionic acid functionalgroups may include, but are not limited to, sulfonic, sulfonimide orphosphonic acid groups. Particles 14 may include all the embodimentsdescribed above in reference to FIGS. 1-4. As is well known in the art,the electrode 70 will preferably be porous (not shown in FIG. 7) toallow appropriate fluid ingress and egress from the electrode.

The electrodes in this embodiment of the invention may utilize the samesupports for the catalyst that are described above. A preferable supportis carbon. The compound binding the catalyst to the particles, and theperoxide decomposition catalyst may also utilize the same materials asthose described above.

The electrodes of this embodiment may be utilized in one or both of theelectrodes in a catalyst coated membrane 86, which may in turn be usedin a fuel cell 83 utilizing a solid polymer electrolyte 80 of anycomposition known the art. Such a fuel cell may optionally includeappropriate gas diffusion media 84 and 85 as necessary to facilitatedistribution of oxidizing and fuel fluids, respectively.

The following test procedures were employed on samples which wereprepared in accordance with the teachings of the present invention.

Test Procedures

Catalyst Coated Membrane Preparation

Various inventive and other solid polymer electrolytes were prepared asdescribed more fully below. When a catalyst coated membrane was neededfrom any of these, it was prepared by placing it between two PRIMEA®5510 electrodes (available from Japan Gore-Tex, Inc., Tokyo, Japan) with0.4 mg Pt/cm² loading in the each electrode. This sandwich was placedbetween platens of a hydraulic press (PHI Inc, Model B-257H-3-MI-X20)with heated platens. The top platen was heated to 160 degrees C. A pieceof 0.25″ thick GR® sheet (available from W. L. Gore & Associates,Elkton, Md.) was placed between each platen and the electrode. 15 tonsof pressure was applied for 3 minutes to the system to bond theelectrodes to the membrane. The resulting catalyst coated membrane wasassembled into a fuel cell as described below for subsequent testing.

Cell Hardware and Assembly

For all examples, standard hardware with a 23.04 cm² active area wasused for membrane electrode assembly (MEA) performance and durabilityevaluation. This hardware is henceforth referred to as “standardhardware” in the rest of this application. The standard hardwareconsisted of graphite blocks with triple channel serpentine flow fieldson both the anode and cathode sides. The path length is 5 cm and thegroove dimensions are 0.70 mm wide by 0.84 mm deep.

Two different cell assembly procedures were used. In the firstprocedure, designated as procedure No. 1, was used in the evaluation ofmembrane chemical durability by an open-circuit-voltage (OCV) holdmethod, which is described as Test Procedure 1. In this cell assemblyprocedure, the gas diffusion media (GDM) used was a microporous layer ofCarbel® MP 30Z placed on top of a Carbel® CL gas diffusion layer (GDM),both available from W. L. Gore & Associates, Elkton, Md. Cells wereassembled with two 20 mil UNIVERSAL® ePTFE gaskets from W. L. Gore &Associates, having a square window of 5.0 cm×5.0 cm, (available fromTekra Corp., Charlotte, N.C.) and two 1.0 mil polyethylene naphthalate(PEN) films hereafter referred to as the sub-gasket. The sub-gasket hadan open window of 4.8×4.8 cm on both the anode and cathode sides,resulting in a MEA active area of 23.04 cm².

The second procedure, designated as procedure No. 2, was used toassemble the cells for accessing power density performance of the MEA,which is described as Test Procedure 2. In this assembly procedure,assembly materials were the same as procedure No. 1, with the exceptionsthat the GDM used was SIGRACET® GDL 25 BC (SGL Carbon Group, Germany),and gaskets were two 10 mil UNIVERSAL® ePTFE gaskets.

All the cells were built using spring-washers on the tightened bolts tomaintain a fixed load on the cell during operation. They are referred toas spring-loaded cells. The assembly procedure for the cells was asfollows:

-   1. The 25 cm² triple serpentine channel design flow field (provided    by Fuel Cell Technologies, Inc, Albuquerque, N. Mex.) was placed on    a workbench;-   2. One piece of ePTFE gasket was placed on the anode side of the    flow field;-   3. One set of the GDM was placed inside the gasket so that the    MP-30Z layer was facing up;-   4. The window-shaped sub-gasket of PEN sub-gasket sized so it    slightly overlapped the GDM on all sides was placed on top of the    GDM;-   5. The anode/membrane/cathode system was placed on top of the    sub-gasket with anode-side down;-   6. Steps (2) through (4) were repeated in reverse order to form the    cathode compartment. The gasket used on the cathode side was the    same as that used on the anode side.-   7. There are total of eight bolts used in each cell, all bolts had    spring washers, Belleville disc springs, purchased from MSC    Industrial Supply Co. (Cat#8777849). The bolts were then tightened    to a fixed distance that previously had been established to provide    a targeted compressive pressure in the active area. For assembly    procedure No. 1, and No. 2, the compressive pressure was targeted at    120 and 200 psi, respectively. Compression pressure was often    confirmed by using Pressurex® Super Low Film pressure paper from    Sensor Products, Inc., East Hanover, N.J.    Fuel Cell Testing

Chemical durability and power density performance of various MEAs wereevaluated. A 95° C. OCV hold condition was developed to evaluatemembrane's chemical durability, and a 110° C. beginning-of-life (BOL)polarization curve was used to access membrane's power densityperformance under automotive operation conditions. These protocols,identified as Test Protocol 1 and Test Protocol 2, are described morefully below.

Test Protocol 1

Materials to be tested were prepared as outlined below in the examples,and then assembled into a cell using the procedure outlined above. Thecell was connected to a test station, conditioned, and then the test wasstarted under test temperature and pressure as outlined below. Theassembled cells were tested in fuel cell test stations with GlobeTechgas units 3-1-5-INJ-PT-EWM (GlobeTech, Inc., Albuquerque, N. Mex.), andScribner load units 890B (Scribner Associates, Southern Pines, N.C.).The humidification bottles in these stations were replaced by bottlespurchased from Electrochem Corporation (Woburn, Mass.). The humidityduring testing was carefully controlled by maintaining the bottletemperatures, and by heating all inlet lines between the station and thecell to four degrees higher than the bottle temperatures to prevent anycondensation in the lines. In all cases the inlet and/or outlet relativehumidity of the anode and/or cathode was measured independently usingdew point probes from Vaisala (Vantaa, Finland) to ensure the inputhydrogen and air were humidified to desired relative humidity (RH) atthe testing temperatures.

The cells were first conditioned at a cell temperature 80° C. with 100%relative humidity inlet gases on both the anode and cathode. The outletgas pressure of both sides was controlled to be 25 psig. The gas appliedto the anode was laboratory grade hydrogen supplied at a flow rate of1.3 times greater than what is needed to maintain the rate of hydrogenconversion in the cell as determined by the current in the cell (i.e.,1.3 times stoichiometry). Filtered, compressed and dried air wassupplied to the cathode humidification bottle at a flow rate of 2.0times stoichiometry.

The cells were conditioned for 2 hours. The conditioning processinvolved cycling the cell at 80° C. between a set potential of 600 mVfor 30 seconds, 300 mV for 30 seconds and open-circuit for 5 seconds for2 hours.

After the above procedure, the cells were set to the life-testconditions. This time was considered to be the start of the life test,i.e., time equal to zero for all life determinations. Specific testconditions in this protocol were (Table 1): cell temperature of 95° C.,50% RH for both hydrogen and air, with a minimum flow rate of 100 and200 cc/min, respectively. Outlet pressure was 25 psig in all cases. Cellpotential was left to be at OCV throughout the life test.

Chemical Degradation Rate

For all the tests the amount of fluoride ions released into the productwater was monitored as a means to evaluate chemical degradation rate.This is a well-known technique to establish degradation of fuel cellmaterials that contain perfluorosulfonic acid ionomers. Product water offuel cell reactions was collected at the exhaust ports throughout thetests using PTFE coated stainless steel containers. Fluorideconcentration in the concentrated water was determined using anF⁻-specific electrode (ORION® 960900 by Orion Research, Inc.). Fluoriderelease rate in terms of grams F⁻/cm²-hr was then calculated. Thenumbers reported herein are the calculated average fluoride release rateover the first 400 hours of testing, or over the life of the test if thetest was stopped before 400 hours.

Membrane Life Measurement

The life of the membrane was established by determining the presence offlaws in the membrane that allow hydrogen to cross through it. In thisapplication, this so-called hydrogen cross-over measurement was madeusing a flow test that measures hydrogen flow across the membrane. Themembrane integrity was first evaluated during testing using an OCV decaymeasurement performed at ambient pressures. In Test Protocol 1, thismeasurement was carried out while the cell remained as close as possibleto the actual life test condition. This ambient OCV decay test wasperformed periodically as indicated by the performance of the cell.Typically, it was performed, the first time, within 24 hours ofinitiation of the life test to establish initial base-line of membrane'sintegrity. After the initial test, this procedure was performed lessfrequently near the beginning of cell life (e.g., once a week), and morefrequently the longer the cell operated (e.g., as often as once per daytoward the end of life). Details of the measurement were as follows:

-   1. The outlet pressure of anode and cathode side was reduced to    ambient;-   2. The anode gas flow was increased to 800 cc/min and the anode    outlet pressure was increased to 2 psi above ambient pressure;    meanwhile, cathode air flow was set to be 0, and outlet flow of the    cathode side was shut off by a valve;-   3. The OCV value was recorded every second for 180 seconds;-   4. The decay in the OCV during this measurement was examined. If    this decay was significantly higher than previously observed, e.g.,    when the open circuit voltage value decayed to less than 250 mV in    less than 30 seconds, a physical flow check was initiated to    determine if the membrane had failed;-   5. If the decay was close to that of the previous measurement, the    life testing was resumed. When a physical flow check was indicated,    it was performed as follows:-   6. The gas inlet on the cathode was disconnected from its gas supply    and capped tightly. The cathode outlet was then connected to a flow    meter (Agilent® Optiflow 420 by Shimadzu Scientific Instruments,    Inc., Columbia, Md.). The anode inlet remained connected to the H₂    supply and anode outlet remained connected to the vent.-   7. The anode gas flow was maintained at 800 cc/min, and the anode    outlet pressure was increased at 2 psi above ambient pressure.-   8. The amount of gas flow through the cathode outlet was measured    using the flow meter.-   9. A failure criterion of 2.5 cc/min was established, so that when    the measured gas flow of H₂ was greater than this value, the    membrane was identified as having failed.-   10. If the criterion for failure was met the test was stopped, and    the membrane life was recorded as the number of hours the cell had    been under actual test conditions when it failed the physical flow    check (>2.5 cc/min). If the criterion for failure was not met, the    cell was returned to testing.    Test Protocol 2

Test Protocol 2 was developed to evaluate BOL performance of MEA underautomotive conditions. In this protocol, the materials were prepared asdescribed below in the examples, and assembled into cells as describedabove. The cells were then conditioned, and subsequently tested usingthe procedure outlined more fully below. The test stations used for thisprotocol were fuel cell test stations with Teledyne Medusa gas unitsMedusa RD-890B-1050/500125 (Teledyne Energy Systems, Hunt Valley, Md.),and Scribner load units 890B. The gas units were modified with additionsof solenoid valves from Parker outside of the humidification bottles.These valves control directions of gas flow so that the cells can betested in wet and dry cycles.

The conditioning procedure used in this protocol was the same asdescribed in Test Protocol 1. After conditioning, a series ofpolarization curves were taken by controlling the applied currentdensity beginning at OCV for 1.5 minutes and then stepping through thefollowing currently density and times intervals: 10 mA/cm² for 1.5minutes, 20 mA/cm² for 1.5 minutes, 35 mA/cm² for 1.5 minutes, 65 mA/cm²for 1.5 minutes, 100 mA/cm² for 1.5 minutes, 200 mA/cm² for 1.5 minutes,400 mA/cm² for 1.5 minutes, 600 mA/cm² for 1.5 minutes, 800 mA/cm² for1.5 minutes, 1000 mA/cm² for 1.5 minutes. Then the following potentialswere applied in steps: 500 mV for 1.5 minutes, 450 mV for 1.5 minutes,400 mV for 1.5 minutes, 350 mV for 1.5 minutes, 300 mV for 1.5 minutes,250 mV for 1.5 minutes, 200 mV for 1.5 minutes, recording the steadystate current density at every step. Then, the steady state currentdensity was recorded while stepping the voltage in reverse, i.e. 200 mVfor 1.5 min, 250 mV for 1.5 min. etc. The average of the two steadystate currents at each potential was used as the reported value.

Specific operation conditions for the polarization curve are summarizedTable 1.

TABLE 1 Operation Conditions for Test Protocols 1 and 2 Minimum Gas CellCell Inlet Dew Point Flow Outlet Pressure Protocol Temp. Potential GasType (° C.) (anode/cathode) Gas Stoic. (anode/cathode) No. (° C.) (V)(anode/cathode) (anode/cathode) (cc/min) (anode/cathode) (psig) 1 95Open H₂/Air 50/50 100/200 N/A 25/25 Circuit voltage 2 110 VariableH₂/Air 80/80 100/200 1.3/2.0 7/7

EXAMPLES

In the examples below, the ion exchange material used to prepare solidpolymer electrolytes was prepared according to the teachings of Wu, et.al in U.S. Patent Application 2003/0146148, Example 5 except thereactants were adjusted to produce a product with equivalent weight ofabout 920.

This polymer had a melt flow index (MFI) that was typically 6±2 g/10 minwith a range between 2 and 12. The MFI was measured by placing a 2160gram weight onto a piston on a 0.8 cm long die with a 0.20955 cmorifice, into which 3-5 grams of as-produced polymer had been placed.Three separate measurements of the weight of polymer that flowed throughthe orifice in 10 minutes at 150° C. was recorded. The MFI in g/10 minwas calculated as the average weight from the three measurements times3.333. To make the ion exchange material more stable, this product wastreated with 500 kPa of a 20% fluorine/80% nitrogen gas mixture at 70°C. for two six hour cycles. The polymer was subsequently extruded,pelletized and acidified using procedures standard in the art. Then itwas made into a dispersion by forming a solution of 20%-30% of the acidform of the polymer, 10-20% deionized water, and balance alcohol in aglass-lined pressure vessel. The vessel was sealed, and the temperaturewas raised to 140° C. at a rate slow enough to maintain the pressure atless than 125 psi. It was held at 140° C. and about 125 psi for 2.5hours. Then, a final solution was obtained by adding sufficient water toproduce a solution the desired water percentage. This ionomer will bereferred to herein as Type 1 ionomer.

For those examples below where an expanded polytetrafluoroethylene(ePTFE) membrane was used it was prepared using the teachings of Hobsonet. al. in U.S. Pat. No. 6,613,203. A membrane similar to the Type 2ePTFE in Hobson was prepared except the processing parameters wereadjusted so the mass per area was 6.5±1.5 g/m2, the thickness wasbetween 15 and 25 microns, the longitudinal matrix tensile strength wasabout 267 MPa (38,725 psi), the transverse matrix tensile strength wasabout 282 MPa (40,900 psi), the Gurley number was between 8 and 12seconds, and the aspect ratio was about 29.

Example 1

A Ce containing peroxide decomposition catalyst bound to carbon usingpolyvinylphosphonic acid (PVPA) was prepared as follows, Ketjen Blackcarbon powder [1.7779 g] that had been previously oven dried andequilibrated to room conditions was placed in a beaker and impregnatedwith a solution consisting of 7.00 g of a commercial 30%polyvinylphosphonic acid solution plus 2.3 g water. After extensivemixing with a spatula, the solid sample was placed in a muffle furnaceand heated in air to 170-200° C. for over 20 minutes, cooled andequilibrated to room conditions, yielding 3.88 g.

3.77 g of this material was slurried in a solution consisting ofCe(III)(NO3)3.6H2O [1.2556 g] dissolved into 20 mL of water and stirredfor about 1 hour. The solid was then filtered under vacuum, washed 2times with water, 1 time with acetone, 2 more times with water, andfinally with acetone and dried in air. The sample then was placed in amuffle furnace and heated in air to 170° C. for 20 minutes followed bycooling, homogenization, and storing in a vial.

Example 2

A Ce containing peroxide decomposition catalyst bound to carbon usingpolyvinylphosphonic acid (PVPA) was prepared as follows. 3.56 grams ofKetjen black carbon EC300J which had been dried in an oven overnight at80 degrees centigrade at a vacuum of 4.3 inches of mercury, then allowedto cool in a covered container, was placed in a beaker. To it was added14.00 grams of polyvinyl phosphonic acid (Diversitec PVPA-UP, 30.8% inwater). The mix was stirred with a glass stirring rod until uniform. Tothis was added 5.03-g of deionized water and that was again stirreduntil uniform. The beaker containing the mix was placed in a vacuum ovenand baked at 198+/−2 degrees C. for two hours with slow nitrogen purge.The oven was then evacuated to 1.8 inches of mercury with continuingpurge.

The resulting slightly agglomerated black powder which weighed 7.5-g wastransferred to a 150-ml beaker and 60-ml of 3N nitric acid was added.The mix was heated to approximately 60 degrees centigrade with stirringby a magnetic stir bar. At the end of 30 minutes this mix was filteredusing #1 Whatman filter paper and a vacuum flask. The filtrate wasrinsed four times with 50-ml of deionized water.

This process was repeated twice more. The final filtrate was baked todryness for 2.5-hrs at 4.4 inches of mercury vacuum. The resulting blackpowder weighed 6.3-g.

All of this powder was combined with a solution made up of 2.55 grams ofCe (NO₃)₃.6H₂O dissolved in 50-ml of distilled water.

This mix was stirred in a beaker on a hot plate at between 60 and 70degrees centigrade for 90 minutes. The mix was then filtered as beforeand rinsed three times with 75-ml deionized water. The resultingmaterial was dried at 80 degrees for 2 hours. The result was a blackpowder weighing 7.45 grams.

X-ray diffraction was performed using a Shimadzu Lab X, XRD-6000 aftergently grinding the powder. The results show no distinct crystallinepeaks, but two broad diffuse peaks at ˜24 and 42 degrees, consistentwith a material that is mostly amorphous, or non-crystalline.

Example 3

A Mn containing peroxide decomposition catalyst bound to carbon using ppolyvinylphosphonic acid (PVPA) was prepared using the same proceduredescribed in Example 2, except Mn(NO₃)₃.6H₂O was substituted for the Ce(NO₃)₃.6H₂O.

(Separately from this Example 3, the inventors also produced catalystswith PVPA and other metals by separately substituting each of thefollowing for the Ce (NO₃)₃.6H₂O of Example 2: Tb(NO3)3.6H2O,Sa(NO3)3.6H2O, Nd(NO3)3.6H2O, Pr(NO3)3.6H2O, and La(NO3)3.6H2O. Thisproduced catalysts containing Mn, Tb, Sa, Nd, Pr, and La, respectively.)

Example 4

A Ce compound without a support was prepared as follows. To 11 grams of32.2% PVPA in water was added an aqueous solution of 8.95 grams ofCerium (III) nitrate hexahydrate slowly with stirring. The resultingprecipitate was stirred at approximately 60 degrees centigrade for onehour then collected on filter paper. The filter cake was removed fromthe paper and stirred with approximately 70-g of deionized water forfive minutes. This process was repeated four times. The final whitesolid was dried four hours at 80 degrees centigrade and 4.5 inches ofmercury. The final product consisted of 6.3 grams of free flowing finewhite powder. X-ray diffraction was performed using a Shimadzu Lab X,XRD-6000 after gently grinding the powder. The results show no distinctcrystalline peaks, but one broad diffuse peak at ˜21 degrees, consistentwith a material that is mostly amorphous, or non-crystalline.

Example 5

In this example, a composite membrane was prepared using the inventiveperoxide decomposition catalysts as a component. An ink was preparedusing ˜2.5 g of the powder prepared in Example 1, 50 g of type 1 ionomerwith 10% solids, 10% water and the balance ethanol, and an additional 47g of ethanol. This solution was passed through a rotor/stator agitatormixer, Model AX200 by Silverson Machines Inc., Longmeadow, Mass.,hereinafter referred to as a Silverson.) for 15 minutes at 10,000 rpm,followed by three times through a Model M-700 Microfluidizer fromMicrofluidics, Newton, Mass. (hereinafter referred to as amicrofluidizer) at 12,000 to 15,000 psi. Then, a solution containing 27%Type 1 ionomer solids, 15% water and that balance ethanol was preparedand cast onto a fluoropolymer treated polyethylene terephthalate (PET)film using a #40 meyer bar. Expanded PTFE was stretched over the coatingwhile it was still wet to effect imbibing. This “first pass” was thendried with a hair dryer. A second solution was prepared by mixing 3.265g of the ink described above with 30 g of 10% Type 1 ionomer solids in10% water with the balance ethanol. This solution was then cast onto thedried first pass membrane using a 7 mil draw down blade. After this“second pass”, the membrane was dried with a hair dryer, removed fromthe backer, stretched over a glass dish, and annealed at 160 C for 3minutes. The thickness was approximately 18 microns. (This produces amaximum theoretical amount, assuming no loss of cerium in processing, of0.086 grams cerium per 100 grams of dry ionomer, i.e., 0.086% Ce per dryionomer.) Subsequently, a CCM was assembled as described above so thatthe side containing the peroxide decomposition catalyst was toward thecathode. The CCM was tested using Test Protocol 1. Testing results aresummarized in Table 4.

Example 6

In this example the same materials and procedures used in Example 5 wasused, except the first pass and second pass solutions were the same.This casting solution was prepared by adding 7.99 g of the initial inkprepared in Example 5 to 39.982 g of 22% Type 1 ionomer, 20% water andbalance ethanol. The first pass was performed with a 7 mill draw downblade, and the second pass was performed with a 4 mil draw down blade.The final thickness of the membrane was approximately 20 microns. (Thisproduces a maximum theoretical amount, assuming no loss of cerium inprocessing, of 0.22 grams cerium per 100 grams of dry ionomer, i.e.,0.22% Ce per dry ionomer.) Subsequently, an CCM was assembled asdescribed above. The CCM was tested using Test Protocol 1. Testingresults are summarized in Table 4. This sample thus had approximatelytwice the amount Ce compound as the previous example.

Example 7

In this example, a membrane with a different concentration of Cecompound was prepared. First, an ink was prepared by adding 1.0945 gramsof the material prepared in Example 2 above to 8.9905 grams of anionomer dispersion consisting of 20.6% solids in deionized water withand additional 7.4807 grams of deionized water. This mix was placed in avial and dispersed using the Silverson at 10,000 rpm for 25-minutes. Theresulting dispersion was placed in the original vial onto a magneticstirrer and a small PTFE coated stir bar was added. The dispersion wasstirred slowly for several hours or overnight to remove bubblesresulting from the high shear dispersion.

The resulting mix was diluted 2:1 with deionized water and stirred. A6.5 gram aliquot of the diluted mix was then combined with 30 grams of22% BD ionomer and mixed again. This solution was used to prepare amembrane as described in Example 5 except a 6 mil draw down blade wasused in the first pass, and a 4 mil draw bar was used in the secondpass. The final thickness of the membrane was approximately 20 microns.(This produces a maximum theoretical amount, assuming no loss of ceriumin processing, of 0.18 grams cerium per 100 grams of dry ionomer, i.e.,0.18% Ce per dry ionomer.) Subsequently, a CCM was assembled asdescribed above. The CCM was tested using Test Protocol 1. Testingresults are summarized in Table 4. The results show the fluoride releaserate (FRR) is lower than a state-of-the-art commercial product(Comparative Example C2), and the performance in BOL is nearlyidentical.

Example 8

In this example, a composite membrane was prepared using the inventiveperoxide decomposition catalysts as a component. 0.59 grams of thematerial prepared in Example 3 that was hot-acid washed using the sameprocedure as described in Example 2 was combined with 3.55 grams of anionomer dispersion consisting of 20.6% solids in deionized water andwith and additional 2.95 grams of deionized water. This mix was placedin a vial and dispersed using a rotor stator agitator (Model AX200 bySilverson Machines Inc., Longmeadow, Mass.) running at 10,000 rpm for25-minutes. The resulting dispersion was mixed with 28.94 grams of BDionomer at 26.92 percent solids using the rotor stator agitator mixer asbefore. This solution was cast onto a fluoropolymer treated polyethyleneterephthalate (PET) film using a 5 mil draw down bar. Expanded PTFE wasstretched over the coating while it was still wet to effect imbibing.This “first pass” was then dried with a hair dryer. The same solutionthen cast onto the dried first pass membrane using a 3 mil draw downblade. After this “second pass”, the membrane was dried with a hairdryer, removed from the backer, stretched over a glass dish, andannealed at 160 C for 3 minutes. The thickness was approximately 20microns, (This produces a maximum theoretical amount, assuming no lossof cerium in processing, of 0.75 grams manganese per 100 grams of dryionomer, i.e., 0.75% Mn per dry ionomer.) Subsequently, a CCM wasassembled as described above. The CCM was tested using Test Protocol 1.Testing results are summarized in Table 4.

Example 9

In this example, the inventive composition was used as a component in anelectrode for application in a fuel cell. An ink was prepared by using˜2.5 g of the powder prepared in Example 1, 50 g of type 1 ionomer with10% solids, 10% water and the balance ethanol, and an additional 47 g ofethanol. This solution was passed through a rotor stator agitator (ModelAX200 by Silverson Machines Inc., Longmeadow, Mass.) for 15 minutes at10,000 rpm, and then three times through microfluidizer at 12,000-15,000psi.

Separately, a concentrated catalyst ink consisting of platinum on acarbon support was prepared as follows: 7.46 g of Pt/C catalyst (typeSA50BK, N. E. Chemcat, Inc., Tokyo, Japan) was mixed with 0.85 gethanol, 86.09 g terbutanol, and 80.62 g of Flemion ionomer ofequivalent weight of 950 (Asahi Glass, Co. Ltd., Tokyo, Japan) in a 2liter glass vessel. The vessel was evacuated and filled with nitrogen 3times, then opened and mixed with a stainless steel spatula, andtransferred to a 200 ml bottle. Then it was mixed with the Silversonagitator for 30 minutes at 10,000 rpm.

A final ink was prepared by adding 8.1 g of the ink containing theinventive compound to 45 g of the Pt/C/ionomer ink. This solution wascast onto an ePTFE membrane using a draw down blade and dried with ahair drier. The final electrode had approximately 0.12 g/cm² Pt. It wassubsequently prepared into a CCM and tested using the proceduresoutlined in Test Protocol 1 except the break-in occurred for 4 hoursinstead of 2 hours. The average fluoride release rate after ˜400 hoursof testing was 4.78×10⁻⁷ g/cm²/hr.

Comparative Example C1

A GORE-SELECT® membrane Series 5700 (W. L. Gore & Associates, EkltonMd.) was used to assemble a CCM as described above. The CCM was testedusing Test Protocol 1. The fluoride release rates were higher than theinventive examples.

Comparative Example C2

A GORE-SELECT® membrane Series 5720 (W. L. Gore & Associates, EkltonMd.) was used to assemble a CCM as described above. The CCM was testedusing Test protocol 1 and 2. The fluoride release rates were higher thanthe inventive examples (Table 4).

Comparative Example C3

In this example, an insoluble Cerium compound is added to a membrane ina concentration range roughly comparable to the inventive materials.Cerium oxide was added to a solution containing 20% Type 1 solids, 20%water, balance ethanol in order to reach approximately 0.02 wt. % Ce.This solution was cast onto a fluoropolymer treated polyethyleneterephthalate (PET) film using 7.5 mil draw down blade. Expanded PTFEwas stretched over the coating while it was still wet to effectimbibing. This “first pass” was then dried with a hair dryer. The samesolution then cast onto the dried first pass membrane using 4.5 mil drawdown blade. After this “second pass”, the membrane was dried with a hairdryer, removed from the backer, stretched over a glass dish, andannealed at 160 C for 3 minutes. The thickness was approximately 21microns. Subsequently, a CCM was assembled as described above. The CCMwas tested using Test Protocol 1. Testing results are summarized inTable 4. Unlike the inventive materials, the soluble Ce in thiscomparative example is mobile in the membrane, and may even wash out ofthe cell completely in very aggressive conditions.

Comparative Example C4

In this example, a soluble Cerium compound is added to a membrane in aconcentration range roughly comparable to the inventive materials.Ce(NO₃)₃-6H₂O was added to a solution containing 20% Type 1 solids, 20%water, balance ethanol in order to reach approximately 0.12 wt. % Ce.This solution was cast onto a fluoropolymer treated polyethyleneterepthalate (PET) film using 8 mil draw down blade. Expanded PTFE wasstretched over the coating while it was still wet to effect imbibing.This “first pass” was then dried with a hair dryer. The same solutionthen cast onto the dried first pass membrane using 5 mil draw downblade. After this “second pass”, the membrane was dried with a hairdryer, removed from the backer, stretched over a glass dish, andannealed at 160 C for 3 minutes. The thickness was approximately 20microns. Subsequently, a CCM was assembled as described above. The CCMwas tested using Test Protocol 1. Testing results are summarized inTable 4. The results show fluoride release rates higher than theinventive materials, and again, unlike the inventive materials, thesoluble Ce in this comparative example is mobile in the membrane, andmay even wash out of the cell completely in very aggressive conditions.

TABLE 4 Results Test Protocol 1 Results Test Protocol 2 Life Ave. Ave. V# of Time FRR* # of at Example tests (hr) (g/cm² · hr) Tests 800 ma/cm²5 1 >810 1.76E−08 — — 6 1 >740 3.28E−08 — — 7 1 >810 1.33E−08 6 0.568 82 >501 1.08E−08 — — C1 1 212 4.02E−06 — — C2 2 >433 1.06E−07 2 0.565 C31 >432 1.26E−07 — — C4 2 >427 4.34E−08 — — *Fluoride Release Rate,calculated as described above.

As can be seen from the results presented in Table 4, the inventiveexamples all provided dramatically better (lower) fluoride releaserates, up to two orders of magnitude better than the comparativeexamples.

1. A solid polymer electrolyte membrane comprising (a) an ion exchangematerial and (b) dispersed in said ion exchange material, a hydrogenperoxide decomposition catalyst bound to a carbon particle support,wherein the hydrogen peroxide decomposition catalyst comprises (i)polyvinylphosphonic acid and (ii) cerium.
 2. The solid polymerelectrolyte membrane of claim 1 wherein said solid polymer electrolytemembrane further comprises expanded polytetrafluoroethylene having aporous microstructure of polymeric fibrils, and said ion exchangematerial impregnated throughout the porous microstructure of theexpanded PTFE membrane so as to render an interior volume of theexpanded PTFE membrane substantially occlusive.
 3. The solid polymerelectrolyte membrane of claim 2 wherein said solid polymer electrolytemembrane comprises a first layer comprising (a) at least one expandedPTFE membrane having a porous microstructure of polymeric fibrils, and(b) at least one ion exchange material impregnated throughout the porousmicrostructure of the expanded PTFE membrane so as to render an interiorvolume of the expanded PTFE membrane substantially occlusive, and asecond layer comprising ion exchange material in the absence of anexpanded PTFE membrane.
 4. The solid polymer electrolyte membrane ofclaim 3 wherein said second layer comprises said peroxide decompositioncatalyst.